1. Field of the Invention
The present invention relates to a heat roller fixing means with the object of shortening the warming up time by supporting a thin heat roller and a pressure roller with an elastic deforming member at the receiving nip.
2. Description of the Prior Art
In an electrostatic recording apparatus such as an electrophotographic copier and a facsimile apparatus, there have been known various systems for heat-fixing a toner image formed on a recording member. To roughly classify fixing systems being popularly utilized at present, there are two systems, a non-contact fixing system in which toner is fixed by heat with radiant energy such as infrared rays, and a contact fixing system in which a heating member is brought into contact with a recording member which holds the unfixed toner thereon and said toner is heated and fixed by the conduction heat radiated from the said heating member. As the fixing means of the latter system, there have generally been known and popularly put into practice a heat roller fixing means comprising a rotating heat roller with a built-in heater and a pressure contact roller which is brought into revolving pressure contact with said heat roller. The contact type fixing system is excellent in thermal efficiency, so that it has the advantages that it operates with a small consumption of electricity and can fix at a high speed; combined with the recent requirements for speeding up of the recording apparatus, there has been an increasing tendency to adopt such a system. On the other hand, this system has the defect that it takes a long time (i.e. a long warming up time) to raise the surface temperature of a heat roller up to the suitable temperature for fixation (150.degree. C.-180.degree. C.) after an electric current is applied to the heater in a heat roller.
Heretofore, in an attempt to shorten the warming up time, it has been possible to decrease this time by approximately one minute by increasing the power to the heating member and making a thin heat roller and decreasing the heat capacity. However, this has produced some problems such as that the consumed power for fixation is restricted in itself (e.g., 1.5 kw or lower) and that the heat roller under load is deformed by the external force mechanically generated by a pressure roller being brought into pressure contact with the thin heat roller. To cope with this problem, for example, there has been devised the method in which sponge rubber having a lower solidity is used as a pressure roller, the nipping width between a heat roller and the pressure roller is widened even if the pressure contact force is weak, and the thickness of the roller is thinned. In this case, however, if such a heat roller remains in contact with a pressure roller and at the fixing temperature for a long period of time, a problem of permanent deformation of such sponge roller may result. In the case that the thickness of a conventional heat roller is made extremely thin, there results a great difference of solidity between the flange portions at the both ends of the roller and the central portion thereof, so that this produces a problem in that the nipping width does not remain even in the longitudinal direction of the roller.